The ability to form and maintain gradients is essential for the study of response of cells to various stimuli. In nature, concentration gradients of different chemicals cause chemoattraction and repulsion in processes including neuronal growth, immune response, and signaling in single cell organisms. Methods for establishing gradients for tissue culture have mostly involved patterning of cell adhesion molecules on glass slides or cover glasses (Dertinger et al., 2002. PNAS 99: 12542-12547). Such methods result in the formation of stable and reproducible gradients; however, they are useful only for adherent cells. Adherent cells can also be exposed to gradients by flowing over the cells a stream with an imbedded gradient of an active agent. However, this method also results in the exposure of the cells to shear stress, potentially creating artifacts and skewing results. In addition, this method is not applicable to non-adherent cells, unless they are made adherent through non-physiological means.
Methods for establishing gradients of chemoattractants and other agents for the study of adherent or non-adherent cells are frequently relatively primitive. For example, Janetopoulus et al. (2004. PNAS 101: 8951-8956) established gradients to study the response of Dictyostelium discodeum cells to chemoattractants by application of the chemoattractant using a micropipette in an open system. The method allows for rapid modification of spatial and temporal stimuli; however, it has a low throughput and the shape of the established gradient is difficult to measure and to reproduce.
There is a need for a device and method for reproducible, high throughput analysis of response of cells, both adherent and non-adherent, to gradients of active agents.